The invention relates to fluorescent red compositions and fluorescent red articles having improved visibility and conspicuity.
It is commonly known that fluorescent colors provide increased conspicuity for visual signaling under most lighting conditions, and particularly under low natural lighting conditions. These conditions occur at dusk and at sunrise and present a challenge for traffic sign manufacturers. If increased conspicuity of an article is desired, the article is often colored with fluorescent colorants. Fluorescent colors allow enhanced conspicuity because the visual contrast that the fluorescent colors create with the environment is greater than that of similar non-fluorescent articles. Fluorescent colored traffic signs are effective at increasing the conspicuity of the signs and, in turn, increase the likelihood of the signs being observed.
Certain conventions have evolved with respect to the color of traffic signs. In the United States, the Manual for Uniform Traffic Control Devices contains the color code for use on public roadways. For example, informational signs may be green or blue, general warning signs will be yellow, construction and maintenance warning signs are orange and stop signs are red. Motorists have become accustomed to these conventions and color purity is important to encourage the appropriate response. Although fluorescent red dyes are available, their chromaticity or color purity can vary from pink to orange in dyed articles and may not have a true red appearance.
In addition to color purity, it is important for highway signage to be visually conspicuous. As the brightness or luminance of a sign increases, the more visually obvious the sign is relative to its background. The luminance of a fluorescing article is the sum of its reflected and emitted light. The greater the contribution from emitted light to total luminescence the brighter the appearance of the fluorescing article. It is therefore desirable to avoid conditions that quench fluorescence.
Various attempts to improve the visibility of signage have been reported. Burns et al., U.S. Pat. Nos. 5,920,429, 5,754,337, and 5,674,622 disclose fluorescent yellow articles comprising two fluorescent dyes dispersed in a polymeric matrix suitable for applying to retroreflective surfaces. The resulting yellow retroreflective articles are suitable for traffic signs.
Nagaoka et al., U.S. Pat. No. 6,048,069 disclose retroreflective sheeting having image elements made from light transmitting prismatic sheeting. An adhesive layer adheres the prismatic sheeting to the retroreflective sheeting and the adhesive may contain a fluorescent red dye.
Sakaya et al., European Patent Application No. 792,907 disclose polyolefin resin films suitable for outdoor use. The films contain fluorescent substances including perylene dyes and a shielding agent to suppress the deactivation of the fluorescent substance under outdoor conditions and from other substances in the film.
Nagaoka, International Application No. PCT/US97/17457 discloses a retroreflective graphic article having an image layer disposed on a retroreflective base sheet and a dye receiving layer disposed on the image layer. The image layer contains a pigment and a fluorescent dye. The fluorescent dye migrates to the receiving layer, thereby reducing adverse effects from the pigment on the visual properties of the dye.
Smith, International Application No. PCT/AU96/00303 discloses a method for making fluorescent dye compositions useful for making luminescent sunlight collectors from a solution of a fluorescent dye and a polymerizable monomer wherein the solution is prepared without additional solvent and with the aid of ultrasonic mixing. The monomer solution is polymerized in a vertical tube to form a luminescent sunlight collector.
The present invention provides compositions, which can form a coating on a substrate, having a red color fidelity substantially free of orange or pink hues. Further, the coatings of the invention have a visual brightness substantially attributable to fluorescent or emitted light with respect to the total light observed from a coated surface. Accordingly, the present invention in one aspect is a fluorescent red composition comprising a red perylene dicarboximide dye having the formula 
wherein R1 and R2 are identical or different C1-C18 alkyl which are unsubstituted or substituted by C1-C18 alkoxy, C1-C18 alkanoyloxy, C1-C18 alkylthio, hydroxyl, phenyl, phenoxy or phenylthio; cyclohexyl which is unsubstituted or substituted by hydroxyl, C1-C5 alkyl, methoxy, ethoxy, C1-C2 alkylthio, C1-C18 alkanoyloxy or C1-C18 alkoxycarbonyl; phenyl which is mono-substituted or di-substituted in the ortho position by C1-C5 alkyl or chlorine or by C1-C5 alkyl and chlorine; or naphthyl; X, Y and Z are each individually chlorine, bromine or xe2x80x94OR3, and R3 is unsubstituted phenyl, or phenyl substituted by cyano, halogen, nitro, C1-C18 alkyl or a mixture thereof, or naphthyl or anthryl; a film forming resin; and a solvent, wherein the composition provides a coating having chromaticity coordinates (x, y) within the area defined by (0.648, 0.351), (0.735, 0.265), (0.629, 0.281) and (0.565, 0.346) in terms of the CIE 1931 Standard Colorimetric System and measured using 0/45 geometry and evaluated with CIE Standard Illuminant D65 and a fluorescence luminance factor of at least about 8.
Another aspect of the present invention is a fluorescent red coating comprising a fluorescent red composition applied to a substrate wherein the coating has chromaticity coordinates (x,y) within the area defined by (0.648, 0351), (0.735, 0.265), (0.629, 0.281) and (0.565,0.346) in terms of the CIE 1931 Standard Colorimetric System and measured using 0/45 geometry and evaluated with CIE Standard Illuminant D65 and a fluorescence luminance factor of at least about 8.
Yet another aspect of the present invention is a fluorescent red retroreflective article which includes a retroreflective substrate having a retroreflective side and a fluorescent red composition disposed on the retroreflective substrate wherein the retroreflective article has chromaticity coordinates (x, y) within the area defined by (0.648, 0.351), (0.735, 0.265), (0.629, 0.281) and (0.565, 0.346) in terms of the CIE 1931 Standard Colorimetric System and measured using 0/45 geometry and evaluated with CIE Standard Illuminant D65 and a fluorescence luminance factor of at least about 8.
A further aspect of the invention is a method for making a fluorescent red article comprising the steps of preparing a fluorescent red composition, applying the composition to a film to form a coating thereon wherein the film is supported by a backing film, removing the backing film and applying the coated film to a substrate having a pressure sensitive adhesive layer to form a laminate.
Another aspect of the invention is method for making a fluorescent red article comprising the steps of preparing a fluorescent red composition, applying the composition to a first side of a film to form a coating thereon; and affixing the coated first side of the film to a substrate to form a laminate.